TARITARI. 263 



into a secondary lagoon of considerable size, showing that it has been formed 

 by the throwing up of the lagoon beach as a dam across a part of the low 

 reef flat, and enclosing it, has formed the secondary lagoon. The bottom 

 of the lagoon is covered with masses of Algfe, and where the bottom 

 has been exposed as on the edges of sinks, or secondary lagoons, it is soft 

 and spongy. 



From the shoi'e to the west of Butaritari a wide mangrove flat extends 

 into the lagoon almost to the channel (PI. 151, figs. 2, 3) ; it is covered 

 with fine silt, composed of coralline Algte and extremely fine coral sand, 

 and scattered over it are large patches and masses of dead Porites, but in situ 

 (PI. 159, fig. 1). On our way to the southwestern spit we also came upon 

 a number of secondary lagoons, formed by the sliutting off of parts of the 

 flat of varying depth, either from the seaside beach shelf or from the lagoon 

 side, by spurs from the outer or inner lagoon edge (PI. 158, fig. 1), or by 

 ridges and dams thrown up in succession at a time when the flat was open 

 to the lagoon and formed a part of its reef flat. One of these secondary 

 lagoons was fully a mile in width (Pis. 159, fig. 2 ; 160, fig. 1). The flats, 

 ridges, and dams are covered with low bushes, grass, and cocoanut trees. 

 Some of the secondary lagoons are hardly to be distinguished from large 

 sinks, surrounded as they are by vegetation (PL 160, fig. 2). Everywhere 

 on the land rim we found Taro sinks. 



On reaching the village of Ukiarinan, on the west face of the island, we 

 came upon a steep coral shingle beach, formed by the breaking up of 

 beach rock conglomerate, and masses of Nullipores and Pocillipores, with 

 fragments of huge Tridacnas, as well as other shells (PI. 151, fig. 4). The 

 breakers pounding upon this material have broken it up into coarse coral 

 shingle. The beach is steep on the lagoon side ; to the rear the ground 

 slopes very gradually towards the immense flat and secondary lagoons over 

 which we walked for a distance of about five miles, and which forms 

 the western extremity of the island on which is Butaritari village. Some 

 of the coral shingle material has become cemented, and forms a coarse 

 beach rock conglomerate or breccia, composed sometimes of rounded frag- 

 ments, and sometimes of more or less angular pieces of beach rock. 



On our way to examine the eastern part of the atoll of Taritari, we 



